/in/foo.c:2:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c:4:1: error: unknown type name 'bool'
 bool f[1001][1001];
 ^~~~